[plt-scheme] get-text-extent problem

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Mon Aug 4 07:54:18 EDT 2008

At Mon, 4 Aug 2008 09:41:24 +0100, "Stephen De Gabrielle" wrote:
> I'm using get-text-extent to determine the width a string to be
> included in a snip,
> (define/override get-extent
>       (lambda (dc x y w h descent space lspace rspace)
>         ;(for-each (lambda (b) (when (box? b) (set-box! b 0)))
>         ;           (list descent space lspace rspace))
>         (let-values (((width height b s) (send dc get-text-extent
> (format "~A" my-string))))
>           (when (box? w) (set-box! w width))
>           (when (box? h) (set-box! h height)))))
> The problem is the width is wider when get-extent calls
> get-text-extent than when get-text-extent is called by the (snip)draw
> method.

When `draw' is called, the snip's font is already set in the DC. When
`get-extent' is called, the font is not automatically set.

So, to get the right size, you need to specify the font in

 (inherit get-style) ....

 (send dc get-text-extent (format "~A" my-string)
                          (send (get-style) get-font))


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